CCNP Learning Note 3-routing section--OSPF

OSPF RIP EIGRP

Categorical IGP no class link state igp no class distance vector IGP no class blending

Encapsulated IP udp520 IP 88

Update address 224.0.0.5-6 224.0.0.9 224.0.0.10 can also neighbor refer to unicast

Update mode timing (30 points) Full complete (30-second timing trigger incremental trigger

Aging (60 min) trigger

AD 110 120 Rollup 5 external 170 Internal 90

Metric Bandwidth hop count 5 K value (default bandwidth delay)

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LSA is divided into 7 categories

The link state protocol is not routed, but the LSA (link state description information) includes the path and topology.

-The LSA in a zone is synchronous and consistent.

-LSA put to LSDB, run SPF algorithm after synchronization to form SPF tree, generate route table based on SPF Tree

Structure of the link state protocol

-Neighbor table formed and maintained via Hello Packet

Neighbor Database

List of neighbors that contain their own recognition

-Topology Table

LSDB

Contains all routers and the networks they are connected to, compared to the routing information advertised by EIGRP neighbor

LSDB content synchronization in the same region

-routing Table

Forward Database

List of best paths to reach

The structure of the link state protocol: to adapt to large networks and isolate a large number of LSA flooding

Network tiering

-Link state protocol requires network tiering

-level consists of 2 layers: backbone area 0. Delivery route

Non-backbone area: The access terminal route is summarized to the backbone.

Regional features:

-Reduce manual summarization of routing entries

-topological changes affect only their own area

-LSA flooding in its own area

-Hierarchical design

Regional terminology:

The non-backbone area must be connected with the backbone area, the anti-ring, the region is similar to the distance vector method to select the path, through the backbone area to know the non-backbone area

ABR area border routers, which are routes connecting zone 0 and non-backbone areas (routers that connect to non-backbone areas are not called ABR) one router belongs to two regions at the same time, and the interfaces belong to different regions. Compare BGP a router can belong to only one region

ASBR to redistribute external routes into routers in OSPF except for the Special Area OFPF stub

OSPF Neighbors:

Hello update time 10 seconds, dead time 40 seconds premise-point-to-DOT network and broadcast

Hello update time 40 seconds, death time 120 seconds premise-NBMA; point to multipoint; point to multipoint non-broadcast

Router Exchange Hello information establish neighbor

Hello package content: Hello & dead time must be the same

Area ID must be consistent

The authentication password must be consistent

The Flag field of the stub region and stub are not called neighbors

The interface MTU must be consistent unless the configuration interface ignores the MTU.IP OSPF MTU Ignor

The interface masks must be identical in the MA network.

Frame Relay Network, isolation multicast will also fail to form a neighbor relationship

ACL filtering packet causes neighbor not being established

Besides, it also contains the router ID unique identity router; neighbor;

Adjacency: adjacency Relationship synchronization LSA. Neighbor relationships, out of sync LSA

whether an adjacency is formed is determined by the OSPF network type

-Dot to Point Wan

A fully contiguous state is formed between neighbors

-Lan Link

Forming a fully contiguous state MA network with the Dr BDR

Point-to-multipoint-to-multipoint non-broadcast neighboring devices form adjacency relationship

With other routers only form a neighbor relationship, bidirectional state drothers

-routing updates and topology information are only passed between routers that form neighboring relationships

-Once adjacency is formed, the LSA is synchronized

-LSA will flood within a region

The OSPF algorithm SPF algorithm

10~8/Interface Bandwidth (route-in-direction interface) unit bps For example, the cost of a 100M link is 1.

LSA ordinal

-Each LSA has an ordinal number in the LSDB

-Sequence numbering scheme is a 4-byte number, from 0x80000001 to 0X7FFFFFFF

-Every 30 taps by the LSA flooding once, ensure the database synchronization, flooding each time, sequence number +1

-Eventually, an LSA loops back from 0X7FFFFFFF to 0X80000001. If this happens, the LSA will be set to 60 for the aging time by the originating router and purged from the LSDB.

-When the router encounters two of the same LSA, it must determine which is up-to-date, that is, the highest number.

LSA ordinal and Time to live

View LSA ordinal: show ip OSPF database

Structure of the link state protocol: LSA

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The router receives an LSA, how can I tell if the LSA already exists locally?

The LSA header information, including 3 information, is exactly the same LSA

Show ip OSPF database

1, type 1--7 class: Router--1 class

2, advertising router: ADV ROUTER

3,lsa Name: Link-id

determine whether an LSA is up-to-date, out of the difference with the serial number, but also can use aging time and calibration and distinguish!!

############################################################################################################# OSPF Package Type ####################

HELLO establishing and maintaining a neighbor Relationship network type decision 10 seconds or 30 seconds

The header message of the DBD LSA 6 messages 3 differentiates whether the same LSA. ; 3 Whether the difference is the newest LSA

LSA type, advertisement router, Link-id; ordinal time-of-life checksum

Link-state request is also an LSA header message

Link-state Update full LSA message

Link-state ACK

Only LSU needs ACK confirmation.

LSU to confirm the LSR.

DBD himself confirmed himself

OSPF Header Format

Version Number	Type	Packet Length	Router Id	Area ID	Check Sum	Authentication Type	Authentication	Date

Version V2--ipv4; V3--ipv6

Type 1-5 5 Types of packages

Routerid Identity Router

Area-id based on interface .... ISIS Region based Router

Checksum to determine if the package has been tampered with

Authentication Type 0: Non-certified, default 1: PlainText 2:MD5

Authentication hash value based on type null password

DATE if DBD: All LSA headers in the local

LSR: Desired LSA Header

LSU: Full LSA

ACK: The LSA header received

Hello Pack: Includes content

Router ID

★hello dead Time

Neighbor received the Hello contains own Routerid

★areaid

Router Priority

DR IP Address

BDR IP Address

★authentication Password

★stub Area Flag

OSPF Router ID

-Each router that runs OSPF has a Routerid

-In LSDB, different routers are identified by Routerid

-By default, Routerid is the highest router active interface IP

-If you configure loop back, he will become a routerid, if there are multiple loops back then select the highest IP

-Configuration process under Router-id x.x.x.x

-It is recommended to use loop back to do Routerid

Routerid configuration is how much is not configured is the loop back IP maximum no loop back to select the active interface IP maximum

Change Routerid to restart the process in order to take effect clear IP OSPF process; This will re-converge and cause a network break.

Routerid the same will not form a neighbor relationship. nonadjacent routers, or different zone routers Routerid can establish neighbors but affect routing delivery.

DR BDR Election

-Use multicast to Exchange hello (priority field)

-Highest priority for DR, second to BDR

-Same priority, compare with Routeid

Priority level

-Interface under command IP OSPF priority number

-Different interfaces may be assigned different values

-Default 1. Range 0-255

-Priority 0 will never participate in Dr BDR elections

-A router is either a Dr or a bdr, or drother

-Dr Bdr non-preemption, but can be set to 0 active waiver, while BDR becomes DR, no higher priority becomes DR, remaining election BDR

-Election time 40 seconds

After the DR/BDR election, Drrother only and the DR, BDR formed adjacent relations.

All routers multicast Hello packets to address 224.0.0.5 so that they can track information from other neighbors, i.e. Dr Will flood LSU to 224.0.0.5

Drother only multicast LSU to all Drother address 224.0.0.6. Only Dr Bdr listens to this address.

All Drother flood LSU to 224.0.0.6, this address can only be received by the Dr Bdr, Drother will discard this multicast address, then Dr flooding LSU to 224.0.0.5, this address all routers can receive, so Dr BDR and all Drother communications.

When there is a link to the LSA with a flood aging time of 3,600 second ordinal +1

When the DR is off, the BDR does not exist, Drother update, the other routers need 40 seconds dead time to know, so drother need 40 seconds to converge

In the case of BDR, Drother update 224.0.0.6 will also be received by BDR, when BDR 4 seconds did not receive Dr about Drother update, BDR will replace Dr, Flood 224.0.0.5. So other routers can converge in just 4 seconds.

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Process

172.16.5.1 172.16.5.3

RA-----------down state---------RB

-----Hello 224.0.0.5-->rb->init State

<----unicast contains RA information-----trigger an update

two-wayState---Unicast contains RB information-"RB also enters two-way state

two-way state uses the priority field in the Hello Routerid to elect the Dr Bdr for 40 seconds, so the two-way will be stuck for 40 seconds, and if you do not need to select the Dr Bdr, move on to the next status .

Exstart State

election Master,master is not necessarily Dr, because Dr uses priority election, Master uses Routerid

Using the Routerid in a DBD message

Ra/|\----------I'll start exhange carry your own Routerid------------->RB

<--no,i would start exchange carrying its own Routerid (address above RA)--

Exchange State

<-------------here is a summary of my LSDB------------------

-------------here is a summary of my LSDB------------------>

Loading State requests each other for what they need

LSR----------The routing-------------required for RA >

<---------RA Required routing-------------LSU

Lsack---------------------------------->

Full state then run SPF to generate the routing table

DBD message, how to realize oneself confirm oneself?

The DBD field includes 3-bit

Whether Init is the initial more if there is a follow-up message if Master is the master

The first DBD flag Field 3 bits is 1, which is flag=7, randomly generating a sequence number. The flag=7 also sends the DBD to the end.

After comparing the Routerid with the end serial number to the Peer Flag= 2. The peer receives 200 of the serial number

Sends the ordinal bit 201 flag=3 until the last message is transmitted to the end flag = 1

Confirm Complete!!!

Cond!!!

CCNP Learning Note 3-routing section--OSPF